Energy in ocean waves exists in two forms: potential energy generating water surface height differences which we see as waves and kinetic energy which moves the water particles back and forth. The energy is split equally between these two forms. More detailed description can be found from Dominic Reeve, Andrew Chadwick and Chris Fleming's book “Coastal Engineering, Processes, Theory and Design Practice”, second edition, 2012, Spoon Press, London and New York, ISBN 978-0-415-58352-7.
Prior art technology includes capturing energy from wave potential energy with different floating objects like buoys. Prior art technology also includes capturing energy from water kinetic energy with various stagnation pressure flap constructions. Prior art technology does not capture both energy types simultaneously in an efficient manner.
Most energy plants are not optimized for capturing energy of both types simultaneously. Since half of wave energy exists in potential form and other half in kinematic form, a lot of energy flux is bypassing current power plants. This makes them inefficient and increases unit cost of produced energy. Also movements opposite to water flow in some areas of the moving objects cause very high internal loads to the structures and unnecessary reaction forces to the supporting structures, requiring uneconomical over-sizing of the structures.
Patent document U.S. Pat. No. 8,253,263B2 discloses an energy plant, which captures both energy types. However, certain problems are related to this prior art structure. The structure includes flaps that are fixed with parallel arms, causing the flaps to have permanently fixed orientation. Not following the velocity profile of water in different depths causes excessive forces to the structures when flap motion reaches either end position and stops. Another problem relates to a rigid float of the structure. Wave crests have arbitrary lengths, and a rigid float causes extreme loads to the proposed support tower when one end is on the wave crest and the other on through.
The prior art solution disclosed in U.S. Pat. No. 8,253,263B2 also relies on extreme conditions survival turning the plant along the wave advancing direction. This orientation is known to produce extreme high loads to a floating object, known in shipbuilding as sagging and hogging, depending on the wave crest and through positions along the floating object, and also pitching movement which causes extreme loads to supports limiting the movement. Incorrectly dimensioned ships without any penetrations break in these circumstances and a ship size object forced to follow a stationary column penetrating through it has severe structural problems on the penetration area and in the column.
There is a further problem which relates to prior art energy plants which are anchored permanently to the sea bed. Tidal changes in water depth reduce radically the energy output of any flap construction in such energy plants because wave flow speed is highest on the surface, going deeper the friction reduce flow speed. Permanent bottom anchoring of a solid flap or wing does not allow the plant to reach the best surface energy flux in high tide. Any fixed anchoring also introduces another power reduction factor, being the angle of incidence between wave crests and plant orientation in waves coming in from arbitrary directions.
Current technology level of wave power plants is still in the testing phase of innovations, and therefore routine maintenance and plant life time economics has not been an important driver. This shows up in the complication of required maintenance: dry docking, diving, towing on shore etc. has to be performed within narrow, calm enough weather windows. Underwater maintenance is impossible in harsh weather due to rapid flows and violent plant movements. The productivity of an energy plant is thus reduced further even due to minor technical problems.
A further problem with prior art wave energy plants relates to currently used gas-pressurized accumulators. The storage capacity available for filtering power ripple is inadequate, causing the output power to alter according to the waves. This makes the wave power difficult to utilize in common grid without additional arrangements.
As a consequence, the prior art wave energy plants do not have optimal efficiency, they are easily damaged in the harsh weather, and they are difficult to maintain.